Electron beam recording and readout on thermoplastic film



April 19, 1966 .1. E. WOLFE ETAL ELECTRON BEAM RECORDING AND READOUT 0N THERMOPLASTIC FILM 7 Sheets-Sfieet 1 Filed Sept. 26, 1961 Fig.1

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April 19, 1966 WOLFE ET AL ELECTRON BEAM RECORDING AND READOUT ON THERMOPLASTIC FILM Filed Sept. 26, 1961 '7 Sheets-Sheet 7 [five/#10215 John E h a/fe fober 6. Fee ves W 64% M24 7/)e/r' Attorney United States Patent 3,247,493 ELECTRON BEAM RECORDING AND READGUT 0N THERMOPLASTIC FILM John E. Wolfe and Robert G. Reeves, Jr., both of Schenectady, N.Y., assignors to General Electric Company,

a corporation of New York Filed Sept. 26, 1961, Ser. No. 140,349 19 Claims. (Cl. 340-173) This invention relates to a new and improved method and apparatus for reading out data stored in the form of grooves or deformations permanently set in the surface of a record member.

More particularly, the invention relates to a data recording and playback device of the type which uses a thin thermoplastic film surface on which permanent deformations in the form of grooves or depressions are placed by direct electron writing in order to record data to be stored and to a new and improved method and device employing a single electron beam apparatus for both recording data and for reading out the data stored in this manner.

A recording device which employs a solid recording medium having a thermoplastic surface on which television pictures and other forms of data can be permanently recorded by direct electron writing has been described in a copending United States Patent Number 3,113,179, issued December 3, 1963, W. E. Glenn, inventor, entitled, Method and Apparatus for Recording, assigned to the General Electric Company. The technique has also been applied to the storage of digital data as well as analog data in forms other than a video picture. For the most part, the known recorders and data storage devices of this type employ a light optical readout arrangement wherein light is passed through the light modifying depressions in the solid recording medium where it is modified by bending, etc. in accordance with the intelligence modulated on the medium. The modified light rays are then imaged through an appropriate masking arrangement to selectively energize a photoelectric device such as a photomultiplier or a vidicon in order to develop an output electric signal. In order to do away with the need for the light optical readout arrangement, the present invention was devised.

It is therefore a primary object of the invention to provide a new and improved method and apparatus employing an electron beam readout of data penrnanently stored in the form of small deformations on the surface of a solid thermoplastic recording medium.

It is another object of the invention to provide a new and improved electron beam readout method and apparatus which is capable of high frequency readout of data stored in the form of small deformations in the surface of a solid thermoplastic recording medium, and which has an improved signal-to-noise ratio of the data read out when compared to existing electro-optical techniques.

In practicing the invention, a method is provided for reading out information stored in the form of small permanent deformations in the surface of a solid recording medium such as the deformations produced in solid thermoplastic material by direct electron writing. The method comprises scanning the deformations in the surface of the medium with a beam of primary electrons, collecting the secondary electrons which are emitted from the surface of the recording medium as a result of the impingement thereon of the primary electron beam, and deriving the recorded intelligence from variations in the number of secondary electrons collected. In practicing this method, a recording playback device is provided which comprises an electron gun assembly having a deflection means capable of deflecting the electron beam of the gun over a Wide deflection angle. The electron gun assembly is sup- 3,247,493 Patented Apr. 19, 1966 ported in a vacuum tight housing along with the solid thermoplastic recording medium to be read out with the gun being positioned in confrontnig relation with respect to the deformations on the surface of the recording medium. A collecting means is positioned within the housing in confronting relation with respect to the recording medium and is disposed to one side of the electron beam path so that it does not interfere with the primary readout electron beam. The collecting means serves to collect secondary electrons emitted from the surface of the recording medium as a result of the impingement thereon of the primary readout electron beam. The secondary electron current produced in the collecting means then provides a measure of the intelligence recorded on the recording medium.

Other objects, features and many of the attendant advantages of this invention will be appreciated more readiiy as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference character, and wherein:

FIGURE 1 is a sectional View of an electron beam readout apparatus constructed in accordance with the invention, and suitable for use in carrying out the new and improved electron beam readout technique;

FIGURE 2 is a partial perspective view of a greatly magnified solid thermoplastic recording plate showing the deformations formed in its surface by means of direct electron writing, and which is to be read out with the apparatus shown in FIGURE 1;

FIGURE 3 is a plan view of the electron beam readout apparatus shown in FIGURE 1;

FIGURE 4 is a sectional view of a portion of the electron gun assembly used in the electron beam readout apparatus, and shows the details of construction of the electron source;

FIGURE 5 is a cross-sectional view of the electron gun assembly taken through plane 5-5 of FIGURE 4;

FIGURE 6 is a perspective view of a movable electron filament source structure comprising a part of the electro gun assembly shown in FIGURE 4;

FIGURE 7 is a schematic diagram illustrating the man ner in which the primary electron beam impinges upon the grooves or deformations in the surface of the thermoplastic film to produce secondary electrons that are emitted from the sides of the groove in directions and quantities determined by the slope of the sides of the grooves;

FIGURE 8 is a schematic diagram showing the directional aspects of the secondary electrons emitted as a result of the primary electron beam;

FIGURE 9 is a schematic diagram which illustrates the physical phenomena involved in producing quantitative differences in the secondary electrons emitted from the deformations occurring in the surface of a solid thermoplastic recording medium by reason of their different slopes;

FIGURE 10 is a characteristic curve illustrating the ratio of the secondary electrons emitted with respect to the primary electrons emitted plotted against the primary electron velocity in volts;

FIGURE 11 is a schematic circuit diagram depicting the servoing aspects of the electron beam readout technique;

FIGURE 12 is a partial plan view of a surface of a solid thermoplastic recording medium having grooves formed thereon by lateral modulation;

FIGURE 13 is a series of cross-sectional views of the lateral modulation recording medium taken through thermoplastic film recording medium wherein the recording in the medium has been achieved by depth or hill and dale modulation of the surface of the medium;

FIGURE 15 is a cross-sectional view of the thermoplastic recording medium shown in FIGURE 14 taken through plane 15-15;

FIGURE 16 is a characteristic curve which illustrates the mode of operation occurring with the depth modulation technique illustrated in FIGURES 14 and 15; and

FIGURE 17 is a schematic circuit diagram of a preamplifier circuit employed with the electron beam readout apparatus shown in FIGURES 1 and 2 of the drawmgs.

The new and improved electron beam readout method is carried out by means of the recorder readout device illustrated primarily in FIGURES 1 through 3 of the drawings. This electron beam writing and readout assembly comprises a housing 11 which is vacuum tight, and which serves to support an electron gun assembly indicated generally at 12 in confroutingrelation with respect to a solid thermoplastic film recording medium shown at 13 in FIGURE 1. As best seen in FIGURE 3 of the drawings which constitutes a plan view of the assembly shown in FIGURE 1, the thermoplastic recording medium 13 comprises essentially a 4 inch by 4 inch plate that is slideably supported in slots formed in the sides of a rectangular opening cut into the periphery of a circular turntable indicated at 14. It should be noted that while it is preferred that the thermoplastic recording medium be in the form of a plate for use in the particular embodiment of the invention herein described, the recording medium could be in the form of a disc, a tape, or some other suitable configuration, and the recording and reading method comprising the present invention would work equally well. The turntable 14 is rotatably mounted within the vacuum tight housing 11 and is adapted to be turned by a suitable crank and gearing arrangement (not shown) to locate the plate 13 over the electron beam Writing and readout assembly 12. The turntable 14 has four such rectangular openings cut in its periphery so that spaced around the periphery of the turntable 14 are four stations adapted to be disposed in succession over the electron beam writing and readout assembly 12. In the particular arrangement shown, there are three solid thermoplastic film recording medium plates 13 positioned in three of the cutout portions around the periphery of the turntable 14, and the fourth position has a fluorescent plate (not shown) supported therein which will'fluoresce when the electron beam from the electron gun assembly impinges upon it. This fluorescent plate can be viewed through a glass wind-ow 15 formed in the top of housing 11 thereby allowing the operator to check the electron beam diameter size, intensity, etc. In order to insert the solid thermoplastic film recording plates in the slots formed in the sides of the cutout portions around the periphery of the turntable 14, a hatch indicated at 16 in FIGURE 3 is provided which can be secured by bayonet fasteners, screws or other suitable fastening means to maintain a vacuum tight enclosure within the housing 11. To assure that the solid thermoplastic recording plates 13 are properly disposed over the electron gun assembly 12 after being rotated into that position by the turntable 14, a latching arrangement indicated at 17 is provided which coacts with a series of pins 18 located in each of the quadrants of the turntable 14 for assuring that the thermoplastic recording plates of the turntable 14 will be properly maintained in confronting position over the electron beam readout assembly 12.

The electron gun assembly 12 can be used to write data to be recorded on the solid thermoplastic film recording medium plates 13 by suitably increasing the voltage of the gun to a higher value than would otherwise be used in reading out data from plates on which information has been previously recorded. When the electron gun assembly 12 is used to record, heat is supplied to the solid thermoplastic film recording medium subsequent to the electron writing to soften the material sufiiciently to permit deformations by reason of the electron writing charges placed thereon, whereby upon cooling the material, the deformations take a permanent form in the surface of the medium. For this purpose, a heating station indicated at 19 is provided within the housing 11 so that subsequent to writing on a solid thermoplastic film recording plate 13, the plate can be rotated by the turntable 14 to position it under the radiant heating means indicated at 1?. Application of the heat and subsequent cooling of the solid thermoplastic recording medium will serve to permanently set the deformations in the surface of the recording medium as described above. During operation of the readout device, the housing 11 is maintained under a vacuum by suitable vacuum equipment (not shown) which operates through a conduit 21 best seen in FIG- URE 1 connected through the underside of the housing 11 in which the turntable 14- is supported. In addition to the above features, because it is desirable to check the quality of the recording on the solid thermoplastic film recording plate 13 with visual means after each writing operation, a Schleiren projection assembly 22 as shown in FIGURE 1 is attached to the housing 11. In the present embodiment of the invention, this assembly is shown as located diametrically opposite the electron gun assembly 12 as shown schematically in the plan view of FIGURE 3. The Schleiren projection assembly is of conventional construction and makes available a means for easily and quickly making a visual check of the quality of the writing on the solid thermoplastic film recording plates 13.

A desired number of the openings in the periphery of the turntable 14 may be loaded with solid thermoplastic film recording plates 13, and a further opening may be; provided with a fluorescent plate inserted therein. This further station allows the electron beam of the electron gun assembly 12 to impinge directly on the fluorescent plate so that its beam spot diameter and its intensity can be viewed through the glass window 15 and correctly ad justed for either the reading or writing operations as described hereinafter. Assuming that the electron gun assembly 12 is adjusted for the writing operation, then one of the solid thermoplastic film recording plates 13 is rotated in position in confronting relationship with respect to the gun assembly by means of the turntable 14. The nature of one form of the writing is illustrated in FIGURE 2 of the drawings wherein a fragmentary perspective view of a solid thermoplastic film recording plate is shown. It is, of course, to be understood that the recording plate is shown in a position which is upside down from that which would exist when the plate is in proper position withrespect to the electron gun assembly 12. The solid thermoplastic recording plate 13 is comprised by a first layer 250E thermoplastic material as described in the above-identified copending Glenn application. One thermoplastic material that is satisfactory for this use is a blend of polystyrene, m-terephenyl, and a copolymer of 95 weight percent of butadiene, and 5 weight percent styrene. Specifically, the composition may be polystyrene, 28% m-terephenyl, and 2% of the copolymer. The thermoplastic film 25 is disposed over a transparent conductive coating 26 that, in turn, is formed over a Mylar, Cronar, or glass base 27. It is desirable that the thermoplastic film 25 and the base member 27 as well as the transparent conductive coating 26 be optically clear. The characteristics of the thermoplastic film 25 are such that when an electric charge pattern is written thereon by the electron gun assembly 12, and upon heating the film 25 the electrostatic forces due to the electron charges on the film form depressions in the surface of the film which upon cooling of the film become permanent. In the heating process, the film is heated to a liquid state, wherein the term liquid i defined t0 be sufliciently fluid to allow the electrostatic forces acting on the electrons to form the depressions in the surface of the thermoplastic film 25. The nature of these depressions is shown at 28 wherein it is seen that the deformations are in the form of grooves made by a method of electron writing known as defocussing, wherein the electron beam of the electron gun assembly 12 has been broadened at 28 and narrowed as at 29 in accordance with the intelligence to be recorded. As will be described more fully hereinafter, it is also possible to impose the modulation intelligence on the surface of the film by depth modulation wherein the grooves are made deeper and shallower in accordance with the intelligence recorded, or by lateral translation of the electron beam from a center line position much in the fashion of the existing phonograph recording techniques. In making the recordings such as those shown in FIGURE 2, the electron gun assembly is first adjusted for the Writing operation where in the electrons are directed upon the thermoplastic film surface at a somewhat higher velocity than is normally used in the readout operation. These high velocity electrons are subjected to either defocus modulation by application of the intelligence signal to the focussing coil of the electron beam writing assembly, lateral modulation by application of the intelligence signal to the deflection coil of the electron gun assembly, or intensity modulation by application of the intelligence signal to the control grid of the electron beam writer. This results in impressing electrons on the surface of the thermoplastic film 12 in desired intelligence conveying patterns. The thermoplastic film plate 13 is then rotated by the turntable 14 to a position under the heating means 19 where the thermoplastic film 25 is rendered sufficiently fluid to allow electrostatic forces in the electron pattern to form the permanent depressions such as those shown in FIG URE 2.

The electron gun assembly 12 is comprised by an electron source 31 supported at one end of a long glass tube 32 that is secured to the housing 11, and surrounded by a magnetic focussing coil 33 and a magnetic deflection coil 34. The end of the glass tube 32 secured to housing 11 is open so that electrons passing through the tube may impinge upon a thermoplastic film solid recording plate 13 supported by the turntable 14 in confronting relation with respect to the electron beam readout apparatus. Secured in the same end of the glass tube 32 by suitable insulating supports are a pair of collecting members 35 and 36 which are positioned in confronting relationship to the solid thermoplastic film recording plate 13 but are each located to one side of the electron beam path so as not to interfere with the primary readout electron beam. The purpose of these collecting members 35 and 36 will be explained more fully hereinafter.

The details of construction of a portion of the electron gun assembly are shown in FIGURES 4 through 6. For the most part, the electron gun assembly is wellknown, particularly with respect to the fabrication and operation of the magnetic focussing coil 33 and the magnetic deflection coil 34. It is essential, however, that the electron gun assembly have a wide deflection angle so that the electron beam can be made to trace over the entire area of the thermoplastic film recording plate 13. For this purpose, the electron source 31 of the assembly has been specially designed, and comprises a removable filament assembly 41 which is shown in perspective in FIGURE 6 of the drawings. This assembly comprises a hollow metallic plug 41 which is held in place by a plurality of studs 42 within the electron source 31. The plug 41 is inserted in the hollow opening of a base member 46. This hollow opening is offset slightly to one side of the axis of the base member 46 so that the plug 41 likewise is offset. Axially secured in the removable plug 41 is an insulating support 43 through which a pair orf conductors 44 and 45 pass. All of these members are press-fit so that they are physically retained in place when the holding studs 42 are drawn up to hold the plug as sembly into position on the base member 46 of the electron source. The filament of the source is a bent back hairpin 47 secured between the conductors 44 and 45, and which is shaped in the form of a loop and doubled back over itself to form a very fine pinpoint source at its outermost point. In order to adjust the position of this pinpoint source of electrons, the removable plug 41 may be rotated slightly thereby resulting in movement of the insulating support 43. Because of the offcenter position of plug 41 and hence the insulating member 43, the pinpoint source 47 will be moved slightly off center thereby facilitating alignment of the electron beam with respect to the remainder of the electrode structures in the electron source. This electrode structure includes a grid electrode 48 that is threadably secured into the base member 46 of the source and has a number of openings the central one of which is aligned over the hairpin filament 47. Disposed over the grid electrode 48 is an anode electrode 49 which has a pointed head 51 disposed opposite the hairpin filament 47, and which is threadably secured within a sleeve that comprises a part of the glass envelope 32. The pointed construction of the accelerating anode 49 greatly facilitates shaping of a fine electron beam, and in addition allows the beam to be swept over a much greater deflection angle than with conventional constructions. FIGURE 5 is a cross-sectional view of the construction of the electron source taken through the plane 55, and illustrates the manner in which the folded back hairpin filament 47 can be properly aligned with the opening in the :grid electrode 48 by mere rotation of the plug 41. The entire structure is sealed tightly with appropriate ring gaskets at points where it is desirable that no leakage occurs so that the space may be evacuated through the glass tube 32. By reason of this construction of electron source 31, taken in conjunction with the magnetic deflection coil, it is possible to deflect the electron beam of the tube over a wide angle in two transverse directions.

With the arrangement shown in FIGURE 1, should it be desired to read out information which has been previously recorded in the above described manner on a thermoplastic recording plate 13, the same apparatus shown in FIGURE 1 will be used with the exception that the electric potentials applied to the accelerating anode preferably are reduced over those employed while the gun is used for writing, although it is possible to read out with the same accelerating potential used for writing. For example, in reading out, an accelerating potential of about 1500 volts would be used with an electron beam spot size of about /2 mil to 1 mil diameter. In writing, however, accelerating potentials of up to 5000 or 6000 volts are employed. Assuming that data has already been recorded in the previously described manner and is desired to be read out with the apparatus shown in FIGURE 1, then if a cross-section were taken of the thermoplastic recording medium 13 having data written in the form shown in FIGURE 2., the cross-section would appear as shown in FIGURE 7 of the drawings. From an examination of FIGURE 7, it can be seen that in cases where the data has been recorded in digital :form a deep or narrow groove having steep slopes would appear as shown at 61 while a shallow, wide groove would appear as shown at 62. It is a physical fact that if the primary readout beam as shown at 63 impinges on the side of the groove 61, secondary electrons will be emitted, and the bulk of the secondary electrons will be emitted from the surface of the groove in a direction which is normal to the slope of the side of the groove as shown at 64. This slope is shown in straightline form in FIGURE 8a, and it oan be seen that the secondary electrons emitted along the vector line 64 will be at some angle a with respect to the impinging readout primary electron beam 63. Considering now the shallow, wide groove shown at 62, if the ape 93 readout beam of primary electrons impinges along the vector line 65, then secondary electrons will be emitted from the sides of the groove in a direction normal to the slope of the groove along the vector line 616. From a consideration of FIGURE 8b of the drawings, it can be appreciated that the secondary electrons emitted along the vector-line 66 will form some angle with respect to the incoming primary readout electrons along the vector line 65, and that this angle 0 will be smaller than the angle or due to the fact that the slope of the sides of the groove 62 is smaller than the slope of the sides of the groove 61. Accordingly, it can be appreciated that the slope of the sides of the groove impose a directional aspect on the secondary electrons emitted as a result of the primary readout electron beam impinging on the thermoplastic film surface.

In addition to the directional character of the secondary electron emission, it can be further shown that .the numberor quantity of secondary electrons emitted will be affected by the angle of incidence of the primary readout electron beam. This phenomena can be best explained in connection with FIIGURE 9 of the drawings wherein the slopes of the two diiferent types of grooves are shown at 61 and 62. Assuming that in the case of FIGURE 9a the primary electrons impinge upon the side of the groove 61 along the vector line 63. These primary electrons or a certain number of them will penetrate varying distances into the surface of the film depending upon their electron velocity. For the purpose of illustration at a selected level of electron energy, the primary electrons will penetrate into the thermoplastic film a distance x as shown. Electrons at this energy level will then produce secondary electrons which are emitted in a direction normal to the sides of the slope 61 along the vector line 64, and will have to travel through a distance y of the thermoplastic film before emitting from the surface of the film. Comparing FIGURES 9a to 9b, it can be appreciated that primary electrons of the same energy level which impinge upon the sides of the slope 62 similarly will enter into the thermoplastic film a distance x where x is equal to x in distance. Electrons at this energy level likewise will produce secondary electrons which will be emitted along a vector line normal to the surface of the slope 62, and hence will have to travel a distance y before reaching the surface of the film. By comparing the two distances y and y, it is can be seen that y is substantially greater than y. Accordingly, fewer numbers of secondary electrons produced by the primary electrons at this energy level will escape from the surface of the groove 62 in the thermoplastic film than will escape from the surface of the groove 61 in FIGURE 9a where the slope of the groove is steeper. For this reason, the slope of the sides of the grooves will determine to a great extent the number of secondary electrons emitted from the surface of the thermoplastic film as a result of the impingement thereon of the primary electron readout beam.

The phenomena described in the preceding paragraph is also illustrated in FIGURE 10 of the drawings wherein the primary electron velocity or energy measured in volts has been plotted against the ratio of the number of secondary electrons emitted to the number of primary electrons emitted. This ratio is identified by the Greek letter delta (6). From an examination of FIGURE 10 it can be seen that the ratio 6 increases almost linearly as the primary electron velocity in volt-s is increased. At some point, that is called the. cross-over point, the number of secondary electrons emitted will equal the number of primary electrons impinging on the surface, that is to say 6:1. Thereafter, as the electron velocity is in creased, the number of secondary electrons will increase over those of the primary up to some maximum value Where, because of the high energy of the primary electron beam, the incident primary electrons are driven so deeply into the thermoplastic film that the secondary electrons resulting therefrom are unable to escape from the 5 surface of the film. Thereafter, the ratio 6 begins to drop as shown until the curve crosses back over the 6:1 line at a point referred to as the second or high velocity cross-over point. In FIGURE 10 the ratio 8 versus elecrrron velocity in vol-ts has been plotted for two different "angles of incidence corresponding approximately to the angle a and the angle 0. For substantially all primary readout electron velocity values, it can be seen that the 6, is considerably greater than 6 and that this phenomena therefore can be employed to determine differences in the slope of the grooves formed in the thermoplastic :film surf-ace. Hence, the diflerence in the values of 6,

Hand 6 may be used in reading out the intelligence rethermoplastic recording medium 13, the collector members 3'5 and 36 are provided as shown in FIGURE 1 of the drawings and in FIGURE 7 of the drawings. By measuring the value of the electron current supplied from the collectors 35 and 36 additively with a summing amplifier and measuring instrument 106 shown in FIG- URE 1, it may be readily determined whether one is operating at the value 5, or 6, as determined by the modulation'imposed in the groove being read out by the primary readout electron beam.

In addition to the above described quantitative measurement provided due to the variation in slope of the grooves formed in the thermoplastic recording medium 13, FIGURE 11 depicts the manner in which a primary read-out electron beam can be made to servo along a particular intelligence bearing groove or deformation using the directional characteristics of the emitted secondary electrons. In FIGURE 11 a primary readout electron beam is depicted at 71' as impinging on one side of a groove T2 formed in the surface of the thermoplastic film. Such grooves will be formed along the entire length of the thermoplastic recording medium so that they would extend into the plane of the paper. In order to read out properly the data recorded in the groove, it is essential that the primary readout electron beam remains centered somewhat on the groove 72 as it is scanned over the length of the groove by a suitable scanning signal from a reading deflection signal source such as indicated in block diagram form at 107 in FIGURE 1. The reading deflection signal source 107 may comprise any conventional electron beam deflection scheme for causing the electron beam to be deflected in two transverse directions so that it will be caused to trace along a groove '72, and will be caused to move from one groove to another groove, such as are shown in FIGURE 2, recorded in a particular data record member. One such suitable deflection scheme is described in copending US. Patent Application Serial No. 822,931 entitled Quick Access Data Reference File, I. E. Wolf-e et al., filed June 25, 1959 and assigned to the General Electric Company. For this purpose, differential collecting means are provided which are comprised by two collector members 35 and 36 and which in conjunction with a differential amplifier 102 shown in FIGURE 1 are capable of deriving a differential signal representative of the number of secondary electrons being collected by each of the respective members. As described above, the bulk of secondary electrons will be emitted along a vector normal to the slope of the side of the groove upon which the primary readout electron beam impinges. Actually, the secondary electrons are emitted in accordance with a cosine distribution pattern centered around the normal to the slope of the groove. Accordingly, the bulk of the secondary electrons are emitted normal to the slope of the groove upon which the primary readout beam impinges as depicted by vectors 73 which represent the direction and numbers of the majority of secondary electrons emitted. In addition certain numbers of the secondary electrons, as determined by the cosine distribution will be emitted in .a direction at right angles to the normal as depicted by the vectors 74. It can be appreciated, however, that the numbers of secondary electrons emitted normal to the slope of the groove far exceed the number of secondary electrons emitted in the reverse direction, and hence, it is possible to derive a directional signal by collecting the secondary electrons on both sides of the groove. For this purpose the output current from each of the collector members is supplied to a differential amplifier 102 shown in FIGURE 1 which develops a differential output signal that can be fed back to the magnetic deflection coil 34 of the electron beam readout assembly to cause the primary readout electron beam 71 to trace substantially along the center line of the groove 72.

A second form of modulation of the intelligence to be recorded on the thermoplastic film recording medium 13 is depicted in FIGURE 12 of the drawings. As shown in FIGURE 12, the deformations or grooves formed in the surface of a thermoplastic film 13 as shown at 7-5 are caused to be laterally transposed to one side or another of a median line 76 by superimposing the modulation intelligence on the energizing signal supplied to the magnetic deflection coil 34; As a consequence of this intelligence modulation, the electron beam will be laterally de-flected across the surface of the thermoplastic recording medium 13 in much the same manner as in a phonognaph record. The manner in which this lateral transformation of the grooves 75 affects the readout of the data modulated or recorded in this fashion is depicted in FIGURE 13 wherein a cross-sectional view is taken through planes AA, BB, CC of FIGURE 12. At point A-A it can be appreciated that readout electron beam depicted by the vector line 77 will produce an abundance of secondary electrons which will emerge along a vector line generally normal to the slope of the side of the groove as shown at 78, and are collected by the collector members to produce an output signal. This output signal is again supplied to the differential amplifier 102 for servoing purposes, and to the summing amplifier 105 to derive the recorded intelligence. However, at point B-B along the groove, the modulation signal has laterally transposed the groove to a position where the readout electron beam 77 does not impinge on the sides of the groove at all but instead impinges on the bottom of the groove where the surface of the thermoplastic recording medium is normal to the readout beam. Because of this reason and the high energy of the primary readout electron beam, there will be a substantial reduction in the number of secondary electrons emitted as a result of the primary readout electron beam, and the signal level will drop substantially. At a further point taken through plane CC of FIGURE 12, it can be seen that the primary readout electron beam 77 will again impinge on the sides of the groove. At this point, the primary electron beam will hit the opposite side or slope of the groove and will produce secondary electrons in the previously described manner which will be emitted along the vector line 79 which is substantially normal to the slope of the groove at this point. In this manner, the lateral transposition of the groove will record the data desired to be stored and read out by the primary electron readout beam.

Still a third form of recording the intelligence modulation on the solid thermoplastic recording medium surface is illustrated in FIGURES 14 and 15 of the drawings wherein the solid thermoplastic film 13 is shown as having a portion of the groove formed at a first depth indicated at 81, and a portion of the groove formed at a second depth indicated at 82. In the example shown in FIGURE 14, a sectional view has been taken of a single groove formed by electron writing showing the two different depths 81 and 82, and in FIGURE 15 two different, separate grooves are shown, one of which is formed at the first depth 81, and the second is formed at the second depth 82. The grooves may be formed in the thermoplastic film in this fashion through intensity modulation of the electron velocity by applying an appropriate modulating signal to the control grid of the electron gun assembly. In reading the data recorded in the manner shown in FIGURES 14 and 15, the readout electron beam shown at 84 is caused to track along the center of the groove in a manner described with relation to FIGURE 7 of the drawings so that it will selectively impinge upon a point having a depth 81 which will be described at depth #1 or upon a depth of the groove having a depth at 82 described at depth #2. In impinging upon the grooves at either depth #1 or depth #2, secondary electrons will be emitted in the manner previously described in numbers determined mainly by velocity of primary readout electron beam measured in volts. FIGURE 16 of the drawings is a plot of ratio of the number of secondary electrons emitted versus the number of primaries plotted against the primary electron velocity in volts. To illustrate the method, entitled Case I, three examples are shown. 'In the first example, the primary readout electron beam velocity is set at a point lower than the first cross-over velocity where the first cross-over velocity is defined as the primary electron velocity where the number of secondaries equal the number of primaries so that their ratio equals one (6:1). For the second example entitled Case II, the readout beam has a primary electron velocity which is between the first and second cross-over points, and in the third example, entitled Case III the primary readout electron velocity is higher than the second cross-over in value. Under the conditions of Case I, the number of primary electrons will exceed the number of secondary electrons so that capacitance existing between the conductive film 83 and the surface of the thermoplastic film will be charged negatively. It should be noted that the capacitance varies for depth #1 and depth #2 due to the variation in thickness of the thermoplastic film for these two points. As a consequence, the surace of the thermoplastic film will be charged negatively to the two different values indicated for Case I readout beam velocity. Under conditions of Case II and because of the fact that the primary readout electron beam velocity is above the first cross-over point, the number of secondary electrons will exceed the number of primary electrons so'that the capacitance between the surface'of the themeplastic film and the conductive film will be charged positively. The value of this charge will be determined by the time required for the electron beam to trace across a particular point. During this time, the capacitance will be charged to the value shown as depth #1 and depth #2 for Case II. In this example, the two depths #1 and #2 are not sufficiently separated with respect to their rato 6 of the secondaries to primaries so that obtaining an adequate readout signal would be difficult. With respect to Case III, however, the primary readout electron beam velocity falls on the steep portion of the slope of the characteristic curve so that as the electron beam scans over the groove in this example, depth #1 will be charged negatively, due to the excess of primary electrons, towards the second cross-over point from its initial primary electron beam velocity point during the transit time of the primary readout electron beam, and depth #2,'because of its greater thickness and hence lower capacitance in the same transit time will be charged to a greater value. Because at this point the slope of the characteristic curve is steeper, there is a much greater difference in the value of 6 for the two points and hence it is easier to obtain a good readout signal differentiating between the two thicknesses at depth #1 and depth #2.

As between Case III and Case I, however, it should be noted that upon subsequent readout cycles there is a tendency for the surface of the thermoplastic film to build up a charge which during the successive reading cycles reaches a point where the signal-to-noise ratio becomes intolerable. This is due to the fact that as the number of primary electrons greatly exceeds the number of secondary electrons under conditions of Case I, during the successive readout cycles the surface is charged toward zero value and readout thereafter becomes impossible. To correct this, it would be necessary periodically to flood the thermoplastic film recording surface with electrons at the first cross-over velocity. Under the conditions of Case 111, the surface will be charged to the second cross-over point at which point further charging becomes impossible. Hence, it is desirable to operate in the vicinty of Case III for readout of the depth modulation of the type shown in FIGURES 14 and 15. In order to obtain the desired readout signal, it is necessary to collect the secondary electrons and read the secondary electron current to the collectors as in the previously described embodiment. However, if desired, the current to the conductive film 83 may be measured in its place by the means indicated schematically in FIGURE 1 by the line 95 and the meter 96, since it is a replica of the collector secondary electron current. It might be noted at this point that successive readout cycles by any one of the techniques described herein can cause a progressive building up of the charge on the thermoplastic recording medium surface so that the output signal-to-noise ratio gradually worsens. To correct for this condition all that need be done is to flood the surface of the thermoplastic recording medium with electrons at either the low or high velocity cross-over points.

The technique for reading out depth modulated grooves described in relation to FIGURES 14 and 15 of the drawings can also be applied to readout slope modulated thermoplastic film recordings such as is illustrated in FIGURE 7 of the drawings. In applying the variation of capacitance readout technique to the varying slope modulated thermoplastic film recording, it is assumed that transit time of the primary readout electron beam would allow suflicient dwell at any particular point along the groove to charge that point to a value determined by the capacitance value of the thermoplastic film at this point. The effect of this dwell time is illustrated in FIGURE 10 wherein it is seen that if the primary readout electron beam is allowed to dwell at a particular point wherein the slope at the sideof the groove forms an angle a with respect to the primary readout electron beam, this point will be charged positively to a value indicated by the arrowhead, and thereby produce a change in the value of 6 equal to A5,. Similarly, by allowing the primary readout electron beam to dwell at a point where the incident primary electron beam forms an angle with respect to the emitted secondary electrons, the point will be charged positively to the point on the characteristic curve indicated by the arrowhead which will produce a change in the ratio 6 equal to A8,. By comparing A6,, and A5,, it can seen that the steeper slopes produce a greater A5 or change in ratio of secondaries to primaries. Hence, by measuring this change in the ratio A6, it is possible to derive an output indication of the intelligence recorded on the surface of the thermoplastic film recording surface. It should be noted, however, that this change in ratio A6 is not so great as the absolute differences in the two ratios for the two different slopes so that the preferred method of readout would be the first method described which measures the ratios for the two different slopes of the recording groove.

It should be noted in all of the readout techniques described that the electron beam is used directly in the readout process so that no limitation on the response time of the system is imposed due to conversion from light to electrical signals and other similar limitations imposed by light optic techniques of reading out from thermoplastic film. Accordingly, it is possible to read out data stored on solid thermoplastic film at much greater rates than were heretofore attainable. Further, because of the rather substantial differences of the ratio of the second aryto-primary electrons emitted for the varying slopes produced in the recording process, and because blemishes and scratches in the substrate of the recording medium do not affect the output signals, a greatly improved signal-tonoise ratio is obtained with the electron beam readout technique. Additionally, the directional character of the emitted secondary electrons make servoing along desired lines. of recorded data a practical process so that high fidelity retrieval of stored information is assured. These characteristics plus the fact that the same electron gun assembly can be used for reading out that is used in writing and recording the information in the first instance makes it possible to produce a recording device which possesses all desirable characteristics of thermoplastic film recording but which is less expensive than thermoplastic film recording devices heretofore available.

A suitable preamplifier circuit for use with the readout arrangements described in previous portions of the specification is shown in FIGURE 17 of the drawings. The preamplifier circuit is adapted to be connected to one of the collector plates such as collector plate 35, for instance, through a double coaxial connector 91 having its outer conductive sheath grounded, and its inner con ductive sheath connected directly to the cathode of a cathode follower amplifier comprised by the first triode section 92, a dual triode 92, 93. The inner conductor 94 of this dual coaxial coupling is connected directly to the control grid of the input cathode follower comprised by the dual triode section 92. A suitable grid bias is supplied from a grid biasing battery 95 coupled through a variable resistor 96 and dropping resistor 97 to the con-. trol grid of the cathode follower triode 92. By this arrangement, the signal-to-noise ratio is maximized. The signal appearing across the cathode load resistor 98 is then applied through a coupling capacitor to the second dual triode stage 93 which is connected as a conventional resistance-capacitance coupled amplifier. The amplified output signal appearing at the anode of the dual triode section 93 is supplied through a resistance-capacitance coupling circuit to a conventional resistance-capacitance coupled pentode amplifier 99 whose output, in turn, is supplied through a cathode follower amplifier fill of conventional construction. Because all of these elements of the preamplifier circuit, the cathode followers 92 and M1 and the resistance-capacitance coupled amplifiers 93 and 99 are conventional in construction and in operation, a further description of their details is not believed necessary.

The output from each of the preamplifiers shown in block diagram form at 196 in FIGURE 1, is connected to a conventional differential amplifier 102 such as described on page 178 of the textbook entitle-d, Electronic Analog Computers, by Korn and Korn, published by McGraw-Hill Book Company, 1952. The output of the differential amplifier is then operatively coupled back through a connection 103 to the magnetic deflection coil of the electron gun assembly in a conventional fashion. A further description of these elements or the manner of their connections is believed unnecessary. Similarly, the output of each of the preamplifiers 160 shown in FIG- URE 1 also is connected through conductors 104 to a summing amplifier 105 such as described on page 11 of the above-identified textbook by Korn and Korn, and the output from the summing amplifier is then supplied to a suitable indicating instrument or recorder 11%. Because these devices are of conventional construction and the manner of their connection is well-known, a further description of these elements is believed unnecessary.

From the foregoing description, it can be appreciated that the invention provides a new and improved method and apparatus which employs an electron beam readout of data permanently stored in the form of small deformations on the surface of a solid thermoplastic recording medium. The new and improved electron beam readout is capable of extremely high frequency readout of data stored in the form of small deformations on the surface of a solid thermoplastic recording medium. In addition, because of the large signals available and the lack of sensitivity to scratches, etc. on the substrate of the thermoplastic recording medium, the signal-to-noise ratio of the readout is greatly improved. Further, by elimination of light optic techniques heretofore required in thermoplastic recording, the electron beam readout method and assemblies are less expensive than the thermoplastic recording devices heretofore available.

Having described several embodiments of the electron beam readout for thermoplastic recording constructed in accordance with the invention, it is believed obvious that other modifications and variations of the invention are possible in the light of the above teachings. It is, therefore, to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.

What We claim as new and desire to secure by Letters Patent of the United States is:

1. A recording playback device for use in reading out information stored in the form of small deformations placed in the surface of a solid thermoplastic film recording medium including in combination an electron gun assembly capable of deflecting its electron beam over a wide deflection angle, means for applying a reading energizing potential to said electron gun having an energy value in the vicinity of the second crossover potential of the recording medium, a vaccum tight housing enclosing said electron gun and said recording medium for positioning the gun in confronting relation with respect to the deformations in the surface of the recording medium, and differential collecting means positioned within said housing in confronting relation with respect to the recording medium and disposed out of the primary electron beam path and on opposite si es of the small deformations in the surface of the solid thermoplastic film recording medium for collecting secondary electrons emitted from the surface of the recording medium upon impingement thereon of the primary readout electron beam.

2. A recording playback device for use in reading out information stored in the form of small deformations in the surface of a solid thermoplastic film recording medium including in combination an electron gun assembly having an electron beam deflection means capable of deflecting its electron beam over a wide deflection angle, means for applying a reading energizing potential to said electron gun having an energy value in the vicinity of the second cross-over potential of the recording medium, a vacuum tight housing enclosing said electron gun assembly and said recordin medium for positioning the gun in confronting relation with respect to the deformations in the recording medium, a set of spaced apart collecting members positioned on opposite sides of the deformations on the surface of said recording medium and disposed outside of the electron beam path for collecting secondary electrons emitted from the surface of the recording medium upon impingement of the primary readout electron beam, a differential output circuit operatively coupled to said collecting members for deriving an output electric signal representative of the quantities of secondary electrons emitted from opposite sides of the deformations for use in servoing the readout primary electron beam along desired deformations in the surface, and a feedback circuit operatively coupled between said differential output circuit and the electron beam deflection means for feeding back corrective signals to said deflection means to cause the electron beam to track along selected deformations of the recording medium.

3. The combination set forth in claim 2 further characterized by an additive output circuit operatively coupled to said collector members for deriving a measurement of the number of secondary electrons collected as indica- 14- tive of the intelligence recorded in the deformations on the surface of the medium.

4. The combination set forth in claim 2 further characterized by a conductive coating on the base of the solid recording medium and an electric output circuit means operatively coupled to said conductive coating for deriving a measurement of the secondary electrons collected by measuring the current flow to the conductive coating to thereby produce an indication of the recorded intelligence.

5. The combination set forth in claim 2 wherein the deformations in the surface of the solid recording medium are in the form of small grooves Whose sides have varying slopes that vary in accordance with the intelligence recorded in the surface of the medium, and wherein the major proportion of the secondary electrons are emitted in a direction normal to the slope of the sides of the grooves and in quantities that vary in accordance with the variation in the slope of the grooves whereby the intelligence recorded in the surface of the medium is read out.

6. The combination set forth in claim 2 wherein the deformations are in the form of grooves whose sides are laterally transposed from a median center-line position in accordance with the intelligence recorded in the surface of the medium, and wherein the major proportion of the secondary electrons are emitted in a direction normal to the slope of the sides of the grooves and in quantities that vary in accordance with the variation in the lateral position of the groove from its median center-line position whereby the intelligence recorded in the surface of the medium is read out.

7. The combination set forth in claim 2 wherein the deformations are in the form of grooves whose depth varies in accordance with the intelligence recorded on the surface of the medium so that the capacitance to a conductive coating formed on the base of the recording medium likewise varies in accordance with the intelligence recorded on the surface of the medium, and wherein impingement of the readout primary electron beam on the respective grooves results in charging the capacitance to a voltage level determined by the electron beam velocity and the thickness of the medium at the point of readout, and deriving a measurement of the secondary electrons collected by measuring the current flow to the conductive coating formed on the base of the recording medium.

8. The combination set forth in claim 1 wherein said differential collecting means comprises at least in part a pair of electron multiplier devices disposed on opposite sides of the small deformations in the surface of the solid thermoplastic film recording medium and whose anodes are exposed to the secondary electrons emitted from the surface of the solid recording medium whereby amplification is obtained of the intelligence signal contained in the secondary electrons.

9. The combination set forth in claim 2 wherein said collecting members comprise at least in part anodes of an electron multiplier which are exposed to the secondary electrons emitted from the surface whereby amplification is obtained for the intelligence signal contained in the secondary electrons.

in. A recording and playback device for recording and reading out information stored in the form of small deformations in the surface of a solid thermoplastic filrn recording medium including in combination an electron gun assembly capable of deflecting its electron beam over a wide deflection angle, a vacuum tight housing enclosing said electron gun and said recording medium for positioning the gun in confronting relation with respect to the surface of the solid thermoplastic film recording medium, differential collecting means positioned within said housing in confronting relation with respect to the recording medium and disposed on opposite sides of the surface of the solid thermoplastic film recording medium and out of the primary electron beam path for collecting secondary electrons emitted from the surface of the recording medium upon impingement thereon of the primary read- .out electron beam during the reading mode of operation, means for applying a reading energizing potential to said electron gun assembly having an energy value in the vicinity of the second cross-over potential of the recording medium, during the reading mode of operation, means for applying a writing potential to the electron gun assembly during the writing mode of operation, and means for heating and subsequently cooling the thermoplastic film recording medium during the writing mode of operation.

11. The combination set forth in claim further characterized by an additive output circuit operatively coupled to said differential collectin-g means for deriving an output signal representative of the number of secondary electrons collected during the reading mode of operation and indicative of the intelligence recorded in the deformations on the surface of the medium.

12. A recording and playback device for use in recording and reading out information stored in the form of small deformations in the surface of a solid thermoplastic film recording medium including in combination an electron gun assembly having an electron beam deflection means capable of deflecting its electron beam over a wide deflection angle, a vacuum tight housing enclosing said electron gun assembly and said recording medium for positioning the electron gun assembly in confronting relation with respect to the recording medium, means for applying writing energizing potentials to said electron gun assembly during the writing mode of operation, means for heating and subsequently cooling the thermoplastic film recording medium during the writing mode of operation to thereby form small permanent deformations in the surface of the recording medium indicative of the intelligence to be recorded, means for applying a reading energizing potential to said electron gun assembly having an energy value in the vicinity of the second cross-over potential of the recording medium, during the reading mode of operation, a set of spaced apart collecting members positioned on opposite sides of the surface of said recording medium and disposed outside of the primary electron beam path for collecting secondary electrons emitted from the surface of the recording medium upon impingement of the primary readout electron beam, a differential output circuit operatively coupled to said collecting members for deriving an output electric signal representative of the quantities of secondary electrons emitted from opposite sides of the deformations for use in servoing the readout primary electron beam along desired deformations in the surface, and a feedback circuit operatively coupled between said differential output circuit and the electron beam deflection means for feeding back corrective signals to said deflection means to cause the primary readout electron beam to track along selected deformations of the recording medium.

13. The combination set forth in claim 12 further characterized by an additive output circuit operatively coupled to said collector members for deriving an output signal representative of the number of secondary electrons collected during the reading mode of operation and indicative of the intelligence recorded in the deformations on the surface of the medium.

14. The combination set forth in claim 12 further characterized by a conductive coating on the base of the solid recording medium and an electric output circuit means operatively coupled to said conductive coating for deriving an output signal representative of the secondary electrons collected by measuring the current flow to the con ductive coating to thereby produce an indication of the recorded intelligence. 1

15. The combination set forth in claim 12 wherein the deformations in the surface of the solid recording medium are in the form of small grooves whose sides have varying slopes that vary in accordance with the intelligence recorded in the surface of'the medium, and wherein the major proportion of the secondary electrons are emitted in a direction normal to the slope of the sides of the grooves and in quantities that vary in accordance with the variation in the slope of the grooves whereby the intelligence recorded in the surface of the medium is read out.

16. The combination set forth in claim 12 wherein the deformations are in the form of grooves whose sides are laterally transposed from a median center-line position in accordance with the intelligence recorded in the surface of the medium, and wherein the major proportion of the secondary electrons are emitted in a direction normal to the slope of the sides of the grooves and in quantities that vary in accordance with the variation in the lateral position of the groove from its median center-line position whereby the intelligence recorded in the surface of the medium is read out.

17. The combination set forth in claim 12 wherein the deformations are in the form of grooves Whose depth varies in accordance with the intelligence recorded on the surface of the medium so that the capacitance to a conductive coating formed on the base of the recording medium likewise varies in accordance with the intelli gence recorded on the surface of the medium, and wherein impingement of the readout primary electron beam on the respective grooves results in charging the capacitance to a voltage level determined by the electron beam velocity and the thickness of the medium at the point of readout, and deriving a measurement of the secondary electrons collected by measuring the current flow to the conductive coating formed on the base of the recording medium.

18. The combination set forth in claim 1% wherein said differential collecting means comprises at least in part a pair of electron multiplier devices disposed on opposite sides of the solid thermoplastic film recording medium and whose anodes are exposed to the secondary electrons emitted from the surface of the solid recording medium whereby amplification is obtained of the intelligence signal contained in the secondary electrons.

19, The combination set forth in claim 12 wherein.

said collecting members comprise at least in part anodes of an electron multiplier which are exposed to the secondary electrons emitted from the surface whereby amplification is obtained for the intelligence signal contained in the secondary electrons.

References Cited by the Examiner UNITED STATES PATENTS 2,692,945 10/ 1954 Beaumont 250-27 2,705,764 4/1955 Nicoll 313-68 2,731,560 '1/1956 Krawinkel 313-68 2,851,521 9/1958 Clapp 178-72 2,888,586 5/1959 Williams 313-68 2,908,836 10/1959 Henderson 313-68 2,985,866 5/1961 Norton 340-173 3,168,726 2/1965 Boblett 340-173 IRVING L. SRAGOW, Primary Examiner. R. G. LITTON, T. W. FEARS, Assistant Examiners, 

1. A RECORDING PLAYBACK DEVICE FOR USE IN READING OUT INFORMATION STORED IN THE FORM OF SMALL DEFORMATIONS PLACED IN THE SURFACE OF A SOLID THERMOPLASTIC FILM RECORDING MEDIUM INCLUDING IN COMBINATION AN ELECTRON GUN ASSEMBLY CAPABLE OF DEFLECTING ITS ELECTRON BEAM OVER A WIDE DEFLECTION ANGLE, MEANS FOR APPLYING A READING ENERGIZING POTENTIAL TO SAID ELECTRON GUN HAVING AN ENERGY VALUE IN THE VICINITY OF THE SECOND CROSS-OVER POTENTIAL OF THE RECORDING MEDIUM, A VACUUM TIGHT HOUSING ENCLOSING SAID ELECTRON GUN AND SAID RECORDING MEDIUM FOR POSITIONING THE GUN IN CONFRONTING RELATION WITH RESPECT TO THE DEFORMATIONS IN THE SURFACE OF THE RECORDING MEDIUM, AND DIFFERENTIAL COLLECTING MEANS POSITIONED, WITHIN SAID HOUSING IN CONFRONTING RELATION WITH RESPECT TO THE RECORDING MEDIUM AND DISPOSED OUT OF THE PRIMARY ELECTRON BEAM PATH AND ON OPPOSITE SIDES OF THE SMALL DEFORMATIONS IN THE SURFACE OF THE SOLID THERMOPLASTIC FILM RECORDING MEDIUM FOR COLLECTING SECONDARY ELECTRONS EMITTED FROM THE SURFACE OF THE RECORDING MEDIUM UPON IMPINGEMENT THEREON OF THE PRIMARY READOUT ELECTRON BEAM. 